Propagating iliofemoral venous thrombosis that occurs despite adequate anticoagulation can be detected by the serial fibrinogen uptake test. Twenty-three patients who were receiving heparin sodium for confirmed iliofemoral thrombophlebitis underwent the serial fibrinogen uptake test. There was an increasing percentage of isotope uptake at the groin and the upper part of the thigh in eight of these patients, three of whom subsequently developed clinical signs, perfusion, and ventilation lung scan findings compatible with the occurrence of pulmonary embolism. The remaining 15 patients had decreasing serial fibrinogen uptake during heparin therapy and no sequelas indicative of pulmonary embolism.

Progressive thrombosis in adequately heparinized patients indicates failure of anticoagulation therapy and, when this occurs, we believe that inferior vena cava interruption should be considered before a first, but potentially lethal, pulmonary embolus develops.